Broccoli growth parameters and level of head infestations in simple and mixed plantings: Impact of increased flora diversification

The impacts of interplanting broccoli, Brassica oleracea var. italica L., with chili pepper, Capsicum annuum L., or yellow sweetclover (YSC), Melilotus officinalis L., on broccoli growth parameters and levels of lepidopteran head infestations were studied during two field seasons (winter & summer). During both seasons, several broccoli growth characteristics (e.g. plant vertical area, whole plant biomass, etc.) were significantly reduced in broccoli‐YSC habitats. However, broccoli heads in broccoli‐YSC habitats did not differ significantly in size from other treatment habitats. Additionally, these heads contained the lowest mean lepidopteran contaminants per broccoli crown during the winter season. During this period, the average number of lepidopteran contaminants per broccoli head was more than twice that in monoculture and pepper intercropped broccoli than in broccoli‐YSC habitats. During the summer experiment, the average number of lepidopteran contaminants per broccoli head was greater in pepper intercropped broccoli than in both monoculture and YSC interplanted broccoli. Potential causes of broccoli growth differences and their relationship to lepidopteran ovipositional behavior are discussed.